1. Field of the Invention
The present invention relates to a radio-frequency tag communication device capable of effecting radio communication with radio-frequency tags, to write and read information on and from the radio-frequency tags.
2. Description of Related Art
There is known an RFID (Radio-Frequency Identification) communication system wherein a radio-frequency tag communication device (interrogator) reads out information, in a non-contact fashion, from small-sized radio-frequency tags (transponders) on which desired information is written. In this RFID communication system, the radio-frequency tag communication device is capable of reading out the information from the radio-frequency tags, even where the radio-frequency tags are contaminated or located at positions invisible from the radio-frequency tag communication device. For this reason, the RFID communication system is expected to be used in various fields, such as management and inspection of articles of commodity.
As one form of application of such a radio-frequency tag communication device, there is known a technique to detect the direction in which the radio-frequency tag is located or exists, For instance, Patent Document 1 discloses an RFID searching device. According to this technique, the directivity of communication with the radio-frequency tag is changed, and the direction in which the radio-frequency tag is located can be detected by detecting the direction in which the directivity of reception is the highest.
Patent Document 1: JP-2000-271229 A
According to the above-indicated prior art technique in which the directivity of communication with the radio-frequency tag is changed to detect the direction in which the directivity of reception is the highest, however, the direction in which the directivity of reception is the highest is not necessarily the direction in which the radio-frequency tag is located. Therefore, an improvement of the accuracy of detection of the direction toward the radio-frequency tag is limited. There has been a need of developing a radio-frequency tag communication device capable of highly accurately detecting the direction in which the radio-frequency tag is located.